The present invention relates to a digital system for measuring an input quantity and, more particularly, to a system using a stepper motor in which the number of steps required by a stepper motor to go from a reference point to a variable point determined by the input quantity are counted to provide a digital representation of the input quantity.
The present invention is, for example, useful in digital communication systems in which an analog sensed value must be converted to a digital value for transmission to a central processing unit or to a data gathering panel for processing thereby. A typical digital communication system is used for controlling the air conditioning systems of buildings. In such air conditioning systems, various analog values such as temperature, humidity and static pressure are measured to indicate the conditions of the spaces or zones controlled by the air conditioning systems. These analog values must be transmitted to a processor so that proper remedial action can be taken if the temperature, humidity or static pressure is not as desired. For example, if the temperature within a room in a building is below setpoint during the winter, the processor, using the analog value of the temperature in the room, will determine that heat must be applied to the room to bring the temperature back up to setpoint. In order for the processor to control temperature, the actual temperature must be communicated to it and it must communicate the appropriate response to the air conditioning equipment controlling that room. Since communication equipment are nearly always digital, the analog value of the temperature must be somehow digitally transmitted to the processor.
A typical prior art system for reading an analgo value and for transmitting a digital representation of that analog value comprises a transducer responsive to the analog value for providing a corresponding analog electrical signal and an analog-to-digital converter responsive to the analog electrical signal for providing the digital output representation. The present invention eliminates the two step process and instead directly converts the analog input quantity into a digital output representation.